Effect of carbohydrate feeding frequencies and dosage on muscle glycogen use during exercise

Nine men were studied during three 4-h cycling bouts to determine the effect of frequency and dosage of solid carbohydrate (CHO) feedings (86 g) on muscle glycogen utilization and exercise performance. In the frequency trial (F), the subjects ingested 10.75 g of CHO along with 200 ml of water at 30-min intervals; in the dosage trial (D), the subjects ingested 21.5 g of CHO with 400 ml of water at 60-min intervals. During the control trial (C), the subjects ingested 400 ml of an artificially sweetened placebo at 60-min intervals. Respiratory exchange ratios were significantly elevated in both trials D and F (P less than 0.05). Blood glucose was significantly elevated in trial D 20 min post-feeding but had returned to control levels by 50 min. In trial F, blood glucose was maintained at a constant level throughout the entire 4 h. In trial C, blood glucose declined steadily during the entire 4 h. Despite the differences in blood glucose levels between the three trials, there were no significant differences in the rate of muscle glycogen utilization in any of the trials (D = 82.9 +/- 6.6 [SE] mmol X kg-1 vs C = 80.9 +/- 6.9 mmol X kg-1 vs F = 74.4 +/- 12.2 mmol X kg-1). In a sprint ride (100% VO2max) to exhaustion at the end of each trial, the subjects performed significantly longer in trial F compared to C (120.97 +/- 9.6 vs 81.0 +/- 7.1 s).(ABSTRACT TRUNCATED AT 250 WORDS)